High probability of false-positive gestational diabetes mellitus diagnosis during early pregnancy

INTRODUCTION: This study aimed to assess the validity of applying the International Association of Diabetes and Pregnancy Study Group (IADPSG) criteria for the diagnosis of gestational diabetes mellitus (GDM) at any time during pregnancy. RESEARCH DESIGN AND METHODS: This multicenter cohort study was conducted at five Japanese facilities from January 2018 to April 2019. The study cohort included women at a high risk of GDM who met one or more of the following IADPSG criteria during early pregnancy: fasting plasma glucose (FPG) ≥92 mg/dL and 75 g oral glucose tolerance test (OGTT) value of ≥180 mg/dL at 1 hour, or ≥153 mg/dL at 2 hour (hereafter early-onset GDM). Women diagnosed with early-onset GDM were followed up without therapeutic intervention and underwent the 75 g OGTT again during 24-28 weeks of gestation. Those exhibiting the GDM patterns on the second 75 g OGTT were diagnosed with true GDM and treated, whereas those exhibiting the normal patterns were diagnosed with false positive early GDM and received no therapeutic intervention. RESULTS: Of the 146 women diagnosed with early-onset GDM, 69 (47%) had normal 75 g OGTT values at 24-28 weeks of gestation, indicating a false-positive result. FPG levels were significantly higher in the first 75 g-OGTT test than in the second 75 g-OGTT test (93 mg/dL and 87.5 mg/dL, respectively; p<0.001). FPG levels were high in 86 (59%) women with early-onset GDM during early pregnancy but in only 39 (27%) women during mid-pregnancy. Compared with false positive early GDM, true GDM was more frequently associated with adverse pregnancy outcomes. CONCLUSIONS: Although women with early-onset GDM were followed up without treatment, the results of repeated 75 g OGTT during mid-pregnancy were normal in about 50%. Our data did not support the adoption of IADPSG thresholds for the diagnosis of GDM prior to 20 weeks of gestation.